This invention relates to a process for preparing polyisocyanate-based polymers, which have an improved ability to dissipate static electrical charge.
The majority of organic polymers are poor conductors of electricity and therefore have a tendency to accumulate static electrical charge. As such they cannot be readily used in application areas which require semi-conductive properties unless further modified.
Polyisocyanate-based polymers are useful in a wide variety of applications. Some of these applications are more sensitive than others to damage or discomfort caused by the accumulation of static electrical charges and their ultimate discharge. Areas where this may be critical include for example packaging of electronic components and medical applications where certain clean room operations require an essentially dust-free environment. Clothing and equipment prepared from or containing polyisocyanate-based polymers may be susceptible to the accumulation of static electricity and therefore will attract or be a means of transporting dust into the clean room or dust-free areas.
It is known for example to incorporate conductive fillers such as fibers, powders and particles into a polymer to enhance its conductivity and thus reduce its potential to accumulate static electricity. However, loadings of such fillers are often in excess of 15 percent or more to obtain the good electrical semi-conductivity. Such high loadings are not beneficial to the polymer and its physical properties and may, for example, increase its brittleness.
In U.S. Pat. Nos. 4,617,325 and 4,618,630 a means of obtaining polyurethane polymers which can dissipate electrical charge is taught by the use of anti-static additives consisting of ionizable salt in combination with "enhancers." The anti-static additive is prepared by dispersing an ionizable salt and enhancer into a polyether polyol. The enhancer compound is a certain carboxylic acid ester or salt of a fatty acid. However, in some instances, the enhancer compound acts as a plasticizer for the polyurethane polymer, altering its properties in an undesirable manner.
For the preparation of certain polyisocyanate-based polymers, the use of polyalkylene carbonate polyols can be advantageous. Polyalkylene carbonate polyols are not readily miscible with the polyether polyols and the anti-static additive described in U.S. Pat. Nos. 4,617,325 and 4,618,630. Polyisocyanate-based polymers made with PAC polyols may be modified to dissipate statical electrical charge by the incorporation of conductive fillers.
It would therefore be desirable to provide a process whereby a polyisocyanate-based polymer formed by the reaction of an isocyanate with an active hydrogen-containing composition containing polyalkylene carbonate polyol and having excellent static electrical discharge properties and good physical properties are prepared.